Biochip assembly and assay method thereof

ABSTRACT

The present invention is directed to a biochip assembly comprising a semi-permeable membrane and an assay method using said biochip assembly for carrying out cell based assays. 
     Ideally, such a method involves measuring the migration of cells in a channel under the influence of an analyte wherein said cells are separated from said analyte by a semi-permeable membrane and said analyte and/or said cells are subjected to controlled flow conditions.

FIELD OF THE INVENTION

The present invention is directed to a biochip assembly comprising asemi-permeable membrane and a method using said biochip assembly forcarrying out cell based assays.

BACKGROUND OF THE INVENTION

The ability to monitor migration of biological cells through tight layerof other cells and tissues is crucial for understanding of mechanism ofmany life threatening diseases and development of modern therapeuticdrugs. This migration is typically triggered by the presence of aparticular chemical either immobilized on a surface or diffused througha tissue.

In inflammatory conditions, for example, the migration of leukocytesfrom blood vessels into diseased tissues is crucial to the initiation ofnormal disease-fighting inflammatory responses. At the same time, thisprocess, known as leukocyte recruitment, is also involved in the onsetand progression of debilitating and life-threatening inflammatory andautoimmunne diseases. Thus, the ability to control the migration ofleukocyte through blood vessels into healthy tissues is an importantpathway for development of therapeutic treatment. This migration iscomplicated by the fact that several leukocyte classes participate inthis pathology (including lymphocytes, monocytes, neutrophils,eosinophils and mast cells) and each class carries out its ownphysiological function. There is the whole range of chronic autoimmunediseases. These include psoriasis, atherosclerosis, rheumatoidarthritis, contact dermatitis, multiple sclerosis, inflammatory boweldisease, hepatitis, sarcoidosis, idiopathic pulmonary fibrosis,dermatomyositis and diabetes. There are also numerous organ transplantrejection conditions such as allograft rejection and graft-versus-hostdisease that are determined to a large extent by the leukocytemigration.

The process by which leukocytes leave the bloodstream and accumulate atinflammatory sites and initiate the disease takes place in threedistinct steps (Lawrence and Springer, 1991, Cell 65:859-73; Butcher E.C. 1991, Cell 67: 1033-36; Springer, T. A. 1990, Nature, 346: 425-33;).It is mediated by chemoattractant receptors, by cell-surface proteins,called adhesion molecules, and by the ligands that bind to these twoclasses of cell-surface receptors. The major types of adhesion moleculesare known as “selecting” “integrins” and “immunoglobulin (Ig) family”receptors.

Each of the three steps is essential for the migration of the leukocytesto target tissues. Blocking these steps has been shown to prevent anormal inflammatory response, and promotes abnormal responses ofinflammatory and autoimmune diseases (Harlan et al., 1992, In vivomodels of leukocyte adherence to endothelium. In Adhesion: Its Role inInflammatory Disease., J. M. Harlan and D. Y. Liu, (eds.), W. H. Freeman& Co., pp. 117-150).

The three steps of leukocyte adhesion and transendothelial migration canbe summarized as follows:

Step 1—Primary adhesion. Leukocytes attach loosely to the blood vesselendothelium and “roll” slowly along the blood vessel wall, pushed by theflow of blood. Leukocyte-endothelium attachment is mediated by cellsurface adhesion molecules called “selecting” which bind tocarbohydrate-rich ligands (“glycoconjugates”) on the leukocyte cellsurface.

Step 2—Activation of leukocytes and migration to the target site.Chemoattractant receptors on the surface of the leukocytes bindchemoattractants secreted by cells at the site of damage or infection.Receptor binding activates the immune defenses of the leukocytes, andactivates the adhesiveness of the adhesion molecules that mediate Step3.

Step 3—Attachment and transendothelial migration. The leukocytes bindvery tightly to the endothelial wall of the blood vessel and move to thejunction between endothelial cells, where they begin to squeeze betweenthese cells to reach the target tissue. This tighter binding is mediatedby binding to adhesion receptors called “integrins” on the leukocytes tocomplementary receptors of the “Ig family” on the endothelium. (The Igfamily molecules are named for their similarity to antibody molecules(immunoglobulins)). Chemoattractant receptors are also involved at thisstage, as the leukocytes migrate up a concentration gradient of thechemoattractant secreted by cells at the target site.

It is increasingly clear that there may be another step precedingprimary adhesion, i.e. preceding step 1, called “margination”. As aresult of margination leukocytes get pushed by the red blood cells tothe periphery of blood vessel, thereby allowing leukocytes to interactwith the endothelium. However, margination is not commonly accepted asyet in the three step migration process described above.

These three steps of receptor-ligand interactions are all required andappear to act in a highly cooperative and coordinated manner to mediateleukocyte adherence to the microvasculature, diapedesis, and subsequentleukocyte mediated injury to tissue in inflammatory disease.

LFA-1 and Mac-1 together comprise the leukocyte integrins, a subfamilyof integrins that share a common beta subunit (CD18) and have distinctalphaL, alpha M and alpha.X (CD11a, b and c) alpha subunits (Springer,1990, Nature 346:425-433). They are required for leukocyte emigration asdemonstrated by an absence of neutrophil extravasation (1) in patientswith mutations in the common beta subunit (leukocyte adhesiondeficiency), and (2) after treatment of healthy neutrophils with amonoclonal antibody (mAb) to the common beta subunit in vivo or invitro.

The integrins LFA (lymphocyte function-associated antigen)-1 and Mac-1on the neutrophil bind to the Ig family member ICAM (intercellularadhesion molecule)-1 on endothelium (Diamond et al., 1990, J. Cell Biol.111:3129-3139). LFA-1 binds to ICAM-2, an endothelial cell molecule thatis more closely related to ICAM-1 than these molecules are to other Igsuperfamily members (Staunton et al., 1989, Nature 339:61-64).

The integrin VLA-4, that contains the alpha.4 (CD49d) subunitnoncovalently associated with the betal (CD29) subunit, is expressed bylymphocytes, monocytes, and neural crest-derived cells, and can interactwith vascular cell adhesion molecule-1 (VCAM-1) (Elices et al., 1990,Cell 60:577). Like ICAM-1 and ICAM-2, VCAM-1 is a member of the Igsuperfamily (Osborn et al., 1989, Cell 59:1203).

Chemoattractants are soluble mediators which activate cell adhesion andmotility and direct cell migration through formation of a chemicalgradient. They are produced by bacteria and numerous cell typesincluding stimulated endothelial and stromal cells, platelets, tumorcells, cultured cell lines, and leukocytes themselves. The cellsresponding to chemoattractants appear to express specific receptors ontheir surfaces which bind the chemoattractant molecules and sense thegradient. Receptor stimulation induces cells to respond via a commonsignal transduction pathway which involves interaction of thechemoattractant-receptor complex with a guanine nucleotide orGTP-binding protein (G protein). This interaction stimulatesphosphatidyl inositol hydrolysis by a phospholipase C, thus generatinginositol phosphates and diacylglycerol. A transient rise in cytosolicfree calcium then activates protein kinase C, and a variety of eventsincluding protein phosphorylation, membrane potential changes, andintracellular pH alterations ensue.

Several of the chemoattractants primarily affecting neutrophils wereamong the first chemoattractants identified. These include thecomplement component C5a, arachidonate derivative leukotriene B₄ (LTB₄),platelet activating factor (PAF), and formylmethionyl peptides ofbacterial origin such as formyl-met-leu-phe (fMLP). Althoughstructurally dissimilar and stimulatory via separate receptors, thesemolecules produce a rapid and marked increase in neutrophil adhesivenessand motility leading to chemotaxis and prominent neutrophil accumulationin vivo. The receptors for C5a and fMLP have been identified andsequenced; cDNA clones for each have also been generated (Gerard andGerard, 1991, Nature 349:614-617). These receptors share many structuralfeatures with one another and members of the “rhodopsin superfamily” ofprotein receptors.

The chemoattractants which predominantly activate and guide monocytesinclude monocyte chemoattractant protein-1 (MCP-1) (Leonard andYoshimura, 1990, Immunol. Today 11:97-101), the RANTES protein (Schallet al., 1990, Nature 347:669-71), and the neutrophil .alpha. granuleprotein CAP37, among others. MCP-1 and RANTES are structurallyhomologous and belong to the subfamily of chemoattractive cytokines thatare defined by a configuration of four cysteine residues in which thefirst two are adjacent (C—C). CAP37's structure is most homologous toproteins of the serine protease family (Peteira et al., 1990, J. Clin.Invest. 85:1468-76).

Compared with neutrophil and monocyte chemoattractants, little is knownabout chemoattractants for lymphocytes. The best characterizedlymphocyte chemoattractants are RANTES and IL-8, which primarily attractmonocytes and neutrophils. Several in vitro studies have describedlymphocyte chemotactic activities in the culture supernatants of mixedlymphocyte reactions and mitogen-stimulated human peripheral bloodmononuclear cells (Center and Cruikshank, 1982, J. Immunol. 128:2563-68;Van Epps et al., 1983, J. Immunol. 131:687).

Although considerable effort has been invested on the study oflymphocyte chemoattractants, they remain poorly characterized relativeto monocyte and neutrophil chemoattractants. Chemoattractants for thelatter cell types, such as MCP-1 and IL-8, have been purified based onthe conventional chemotaxis assay, sequenced, and cloned. However, nomolecule identified primarily as a lymphocyte chemoattractive factor hasbeen sequenced and cloned.

The devices for studies and monitoring of transmigration of cells arewell known in the fields of cell biology, life science, medicine,pharmaceutical and the area of drug development. There are also devicesfor filtering, growth and grouping of cells in these fields.

The most widely used assay is the Boyden Chamber assay, in which amicroporous membrane divides two chambers, the lower containing the testchemoattractant and the upper containing the cells, e.g. lymphocytes.The microporous membrane is commonly nitrocellulose or polycarbonate,and may be coated with a protein such as collagen. The distance ofmigration into the filter, the number of cells crossing the filter thatremain adherent to the undersurface, or the number of cells thataccumulate in the lower chamber may be counted.

Such a Boyden chamber is also known as a transwell chamber. The chamberis made of well divided into two compartments, the upper and lowerchamber, by a filter containing pores. A chemoattractant or othersolution is placed in the lower chamber and the suspension cell isplaced in the upper chamber. Cells can then migrate through the pores,across the thickness of the filter, and toward the source ofchemoattractant. Cells that migrated across the filter and attached tothe underside are then counted. In some assays the membrane is coatedwith Extra-Cellular Matrix (ECM) proteins (e.g. laminin, collagen,fibronectin) and then with endothelial cells (EC). A variety of devicesof this class as well as the method for the transendothelial assay aredescribed in U.S. Pat. No. 5,514,555 (Springer).

Boyden chambers are commonly used for studies of disease and also forthe development of drugs for disease treatment. Here we list someexamples of these applications:

Prostate cancer: It is not fully understood at present time themechanism of the bone metastasis. However, interaction between cancercells and bone environment (extra cellular matrix: ECM) seems criticalfor the process [Chen, N., et al., A Secreted Isoform of ErbB3 PromotesOsteonectin Expression in Bone and Enhances the Invasiveness of ProstateCancer Cells. Cancer Res, 2007. 67(14): p. 6544-8]. The ability ofprostate cancer cells to penetrate a synthetic basement membrane wasassessed in a Matrigel-Boyden chamber invasion assay (BD Biosciences).

Allergy inflammation: the typical study is based on the eosinophilsmigration. Assay performed in a 48-well microchamber (neuroprobe) [Wong,C. K., P. F. Cheung, and C. W. Lam, Leptin-mediated cytokine release andmigration of eosinophils: Implications for immunopathophysiology ofallergic inflammation. Eur J Immunol, 2007].

Migration of vascular smooth muscle cells: key step in diseased arteriesand may be controlled by ECM [Koyama, N., et al., Heparan sulfateproteoglycans mediate a potent inhibitory signal for migration ofvascular smooth muscle cells. Circ Res, 1998. 83(3): p. 305-13].

Chemotactic ability of dental plaque: Whole plaque suspensions werechemotactic for polymorphonuclear leukocytes [Miller, R. L., L. E.Folke, and C. R. Umana, Chemotactic ability of dental plaque uponautologous or heterologous human polymorphonuclear leukocytes. JPeriodontol, 1975. 46(7): p. 409-14].

Boyden chambers/Transwell chamber and closely related devices areavailable from a number of vendors such as BD Biosciences; Corning;Neuroprobe; Millipore. Despite this, Boyden Chamber assays are typicallyassociated with certain shortcomings. These include:

-   -   Intravital microscopy studies have suggested that leukocytes        transmigration occurs over a time frame of minutes. In contrast,        the readouts of most Boyden chamber transfilter assays are taken        1-4 hours after cell introduction. This excessive time span is        necessary in order to get reasonable statistics of cell        migration.    -   No physiological flow can be established in this assay thus is        not possible to monitor cells though all stages of leukocyte        recruitment.    -   There is no control of the gradient: chemokine diffusion in the        body might be different than in vitro as it takes longer to get        a cell migration on in vitro assays.    -   Changes in cell morphology during chemotaxis cannot be observed        in real-time (because cells transmigrate through the filter).

In addition, Boyden chamber assays cannot readily answer many questionsrelated to the leukocyte migration. This is particularly true for themolecular and cellular mechanism of the chemokine-inducedtransendothelial migration step of leukocytes that still have not beenfully elucidated. It is not clear at all if positive, negative or anychemokine gradients are involved and how such gradients may physicallypersist in relation to the endothelium. Initially it was thought thatchemokines form soluble gradients across the blood vessel EndothelialCells (ECs). However, in blood even a short persistence of a solublechemokine gradient is not feasible because the constant flow of plasmaremoves the soluble chemokines from the site of their production.Therefore, it has been suggested already over a decade ago that onlythose chemokines that have been physically retained (immobilized) on theluminal membrane, for example by the glycosaminoglycan (GAG) residues ofglycoproteins, may be able to effectively induce the integrin activationof the rolling leukocytes [Rot, A., Contribution of Duffy antigen tochemokine function. Cytokine Growth Factor Rev, 2005. 16(6): p. 687-94].It is known though that a gradient of chemokine can direct cells and itis also well established that ECs protein receptors are necessary forcell adhesion.

There are other known assay types of assays for studies of cellmigration. For example, the Dunn chamber assay comprises concentricrings separated by a bridge. The inner ring is filled with medium andthe outer ring is filled with chemoattractant solution. Cells arecultured on a coverslip and placed upside down onto the Dunn chamber.The assays allow observation of migrating of cells towards the gradientformed between both rings.

Another area of applications that is broadly related to the area oftransmigration is the growth of mammalian cells. A number of methods forculturing mammalian cells of different tissue origins have beenreported. However, many of these cells are difficult to grow in vitroand, when grown, are not morphologically similar to in vivo tissue. Itwould be desirable to produce a tissue and cells which aremorphologically similar to their in vivo counterpart for in vitrotoxicology and other studies (for example, transepidermal drugtransport).

Similarly there are requirements for tests of cells under continuousflow conditions resulting from the area of toxicity. Once identified,candidate drugs or modulators are usually evaluated for bioavailabilityand toxicological effects (Lu, Basic Toxicology, Fundamentals, TargetOrgans, and Risk Assessment, Hemisphere Publishing Corp., Washington(1985); U.S. Pat. No. 5,196,313 to Culbreth and U.S. Pat. No. 5,567,592to Benet). Traditionally, early stages of drug discovery and developmenthave concentrated on optimizing binding and potency of experimentalcompounds. Typically, animal studies are performed on late stagepre-clinical drug candidates to characterize pharmacokinetics (PK),pharmacodynamics (PD) and physiological toxicity. However, animalstudies are costly, time-consuming and are limited, by throughput, tocharacterize no more than a few compounds. Furthermore, several drugshave shown unanticipated or unpredicted side effects only after reachingclinical trials or wide-scale release to the public. The pharmaceuticalindustry has the ultimate goal of replacing animal studies with in vitrotests that are validated, predictive models for human toxicity and drugdynamics. More recently, the industry has set a medium-term goal ofcreating high-throughput, in vitro tests that annotate candidatecompounds with adsorption, metabolism and toxic (hereinafter referred toas “ADMET”) predictive parameters.

The toxicology of a candidate modulator can be established bydetermining in vitro toxicity towards a cell line, such as a mammalian,including human, cell lines. Candidate modulators can be treated with,for example, tissue extracts, such as preparations of liver (such asmicrosomal preparations) to determine increased or decreasedtoxicological properties of the chemical after being metabolized by awhole organism. The results of these types of studies are oftenpredictive of toxicological properties of chemicals in animals, such asmammals, including humans. Current methods designed to model drugabsorption in vivo involve growing a confluent layer of cells on aporous matrix that allows the test compound to permeate through the celllayer and matrix to a bottom well. It is desirable to carry out many ofthese measurements under conditions of continuous flow. These wouldmimic better the real physiological conditions. The complexity andinterplay of biological processes that must be simulated to predict theADMET properties of a compound far exceed the capabilities of currentlyavailable methods and tools. For example, when a patient takes a drug,it must first pass through the gastrointestinal tract and penetrate intothe bloodstream. The drug must then survive oxidative modifications inthe liver and get to the desired site (e.g., target organ or primarytumor) in a sufficient therapeutic concentration. Even if thesebiological functions could be faithfully reproduced in vitro, adifficulty remains in getting the capacity and format of the assay tofacilitate testing and analysis of thousands of compounds. Ideally, theassays should be versatile enough to not only measure the enzyme cascadeactivity inside any living or whole cell, no matter what its originmight be, including cancer cells, tumor cells, immune cells, braincells, cells of the endocrine system, cells or cell lines from differentorgan systems, biopsy samples etc., but should also be able to detectand measure the permeability of the cell to the candidate compound, aswell as the metabolic activity of the cell on the candidate drugcompound. Methodologies are desired that will allow for the more rapidacquisition of information about drug candidate interactions withenzymes that may potentially metabolize the candidate drug, earlier inthe drug discovery process than presently feasible. This will allow forthe earlier elimination of unsuitable compounds and chemical series fromfurther development efforts, and also give an investigator insight as tothe nature of metabolites with potential biological activity derivedfrom the candidate drug. A parallel flow chamber may be used for thispurpose. However, there are several disadvantages when using theparallel chamber. For example, the parallel flow chamber requires asubstantial amount of the drug candidate for the experiment.Furthermore, setting up the experiment is often time consuming andrather complex.

By way of example, liver hepatocytes express a family of enzymes calledcytochromes. One subfamily of cytochromes is known as cytochrome P450.The cytochrome P450 enzyme (CYP450) family comprises oxidase enzymesinvolved in the xenobiotic metabolism of hydrophobic drugs, carcinogens,and other potentially toxic compounds and metabolites circulating inblood. Efficient metabolism of a candidate drug by a CYP450 enzyme maylead to poor pharmacokinetic properties, while drug candidates that actas potent inhibitors of a CYP450 enzyme can cause undesirable drug-druginteractions when administered with another drug that interacts with thesame CYP450. See, e.g., Peck, C. C. et al, Understanding Consequences ofConcurrent Therapies, 269 JAMA 1550-52 (1993). Accordingly, early,reliable indication that a candidate drug interacts with (i.e., isabsorbed by, metabolized by, or toxic to) hepatocytes expressing CYP450may greatly shorten the discovery cycle of pharmaceutical research anddevelopment, and thus may reduce the time required to market a candidatedrug. Consequently, such earlier-available, reliable pharmacokineticinformation may result in greatly reduced drug development costs and/orincreased profits from earlier market entrance. Furthermore, suchearlier-available, reliable pharmacokinetic information may allow acandidate drug to reach the public sooner, at lower costs than otherwisefeasible. Accordingly, extensive pharmacokinetic studies of druginteractions in humans have recently become an integral part of thepharmaceutical drug development and safety assessment process, e.g.,Parkinson, A., 24 Toxicological Pathology 45-57 (1996).

Thus, despite the advances made to date, there remains a need to provideimproved systems for carrying out cell based assays.

SUMMARY OF THE INVENTION

The invention provides method and devices for performing cell basedassays and cell tests.

According to a first aspect of the invention, there is provided a methodfor measuring the migration of cells in a channel under the influence ofan analyte wherein said cells are separated from said analyte by asemi-permeable membrane and said analyte and/or said cells are subjectedto controlled flow conditions. Essentially, the semi-permeable membraneis mounted in the channel and acts as a divider wall defining a samplechannel and an analyte channel.

An objective of the invention is to provide a system and method for thestudy of the migration of the cells under conditions mimicking moreclosely in-vivo situation than some of the currently available systemsand methods.

A further objective is to provide a system and method for the study oftransmigration of the cells through a layer of cells under conditionsmimicking more closely the in-vivo situation, such as for example theconditions of the continuous flow modeling shear stress on cells,conditions of the pulsating flow modeling conditions of pulsating shearstress.

Another objective is to provide a system and the method for the study ofcell-ligand interactions, such as the binding of cells to ligands, andcell to cell interactions such as cell to cell binding and adhesion.

A still further objective of the invention is to provide the system forstudies of the cell response or cell function to drug or drugcandidates. This response or function may include any of the followingby way of example. The test compound may: (1) kill or decrease theviability of the test cell; (2) be metabolized or chemically altered bythe test cell; (3) pass through the test cell unchanged, (4) beunreleasably absorbed by the test cell; (5) cause the movement of thetest cell through the membrane or substrate surface; or (6) cause thedetachment of the test cell from the membrane or substrate surface.

The present invention aims to address at least some of the aboveobjectives.

Ideally, the migration of cells is transmigration and the method of theinvention facilitates the transmigration of cells through thesemi-permeable membrane.

Ideally, the sample cells and/or analyte are introduced at a controlledsteady flow rate across the channel/biochip. In this way cells may bedelivered across the semi-permeable membrane wherein analyte is presenton the opposed surface thereto.

Ideally, such a channel has a width in the range from approximately0.005 to 20 mm, more preferably in the range from approximately 0.1 to10 mm and a depth in the range of from approximately 0.005 to 3 mm, morepreferably in the range from 0.05 to 0.5 mm. According to oneembodiment, the channel has a width of approximately 100 to 500 microns.It will be understood that the width and the depth of the channel do notneed to be constant all across its entire length, and indeed may changeconsiderably between different parts of the channel. The advantage ofthis is that the assembly may be used to mimic situations wherecapillaries or other portions of a patients body might be constricted.For examples, blocking if the arteries and the like, may be easilystudied. The cross-sectional area or bore of the channel may becylindrical or non-cylindrical. Optionally, the bore size may be chosento mimic the bore size of capillaries or venules of a human.

Ideally, the method takes place in an elongate enclosed channel having asemi-permeable membrane mounted therein. It will be understood thechannel may be a microchannel, preferably an elongate enclosedmicrochannel. In this manner, the semi-permeable membrane may act as adivider wall in the elongate enclosed channel, separating the samplechannel from the analyte channel. Alternatively, two or more elongateenclosed channels are connected by the semi-permeable membrane,

Many different assays (e.g. monitoring cell transmigration in achannel/biochip etc) may be carried out and examples of such assays areexpanded on below.

Preferably, said cells are present on at least one side of saidsemi-permeable membrane and said analyte is present on the opposedsurface thereto.

In the method, the sample cells and/or the analyte are ideallyintroduced into the channel at a controlled steady flow rate. Accordingto one embodiment, said cells or said analyte on one side only of saidmembrane is subjected to controlled flow. According to an alternativeembodiment, said cells or said analyte on both sides of said membraneare subjected to controlled flow.

It will be understood that said analyte may be a reagent liquid or gel.Thus, the analyte may be a chemoattractant, a toxic substance and/or apharmaceutical preparation. The reagent gel may be in the form of asolid or semi-solid gel. For example, the reagent liquid may compriseECM gel containing IL-8. It will also be understood that the reagent incertain cases may be a placebo.

According to a preferred embodiment of this aspect of the invention, themethod further comprises forming a layer of seeded cells adjacent to atleast one side of said semi-permeable membrane. Ideally, said layer ofseeded cells is formed on the semi-permeable membrane prior to use andsaid semi-permeable membrane with seeded cells is mounted in the channelprior to use. The seeded cells may form either a confluent ornon-confluent layer adjacent to at least side of said semi-permeablemembrane. Such seeded cells may be endothelial cells.

In another embodiment of this aspect of the invention, the methodfurther comprises coating at least one side of the semi-permeablemembrane with one or more substances which effect cell function prior toforming a layer of seeded cells on said semi-permeable membrane.Ideally, such substance promotes adhesion of cells. Such substances maybe in any form, such as a gel, liquid etc.

The method may also comprise a further step of coating the internal boreof the channel prior to use with a substance which interacts with saidseeded and/or sample cells. Such a substance is ideally a cell adhesionmolecule and/or a cell transmigration substance. To facilitate theattachment of these substances, the walls of the channel may be treated,e.g. by plasma treatment, so that they become hydrophilic.Alternatively, they may be coated by a hydrophilic coating such asliquid silicon. Such a hydrophobic coating ensures that cells do notadhere to the walls of the channel and detrimentally effect the results.

In one application of the method the interaction between said seededcells and said sample cells is monitored and/or recorded.

In another application of the method, the physiological function of saidseeded cells is monitored and/or recorded.

In yet another application of the method, the physiological function ofsaid seeded cells is measured as a function of the shear stress withinthe channel.

In a still another application of the method, the method comprisesintroducing analyte to said channel and monitoring and/or recording theresponse of said seeded cells and/or sample cells to said analyte, interms of adsorption, metabolism and/or toxicity.

In another application, the method comprises measuring cell to cellinteractions and cell to analyte interactions.

It will be understood that the flow conditions may be sustained by apressure driven pumping system or a positive displacement pumping systemor any other suitable means.

In a preferred embodiment of the invention, the method comprises causingsample cell containing liquid to flow in at least one elongate enclosedchannel having a semi-permeable membrane mounted therein, therebydelivering sample cells against the semi-permeable membrane having areagent liquid on the opposed surface thereto.

According to a second aspect of the invention, there is provided abiochip assembly for carrying out assays with living cells wherein theassembly comprises at least one elongate enclosed channel having asemi-permeable membrane mounted therein.

Ideally, the assay is a transmigration assay and the method involvesmeasuring the transmigration of cells.

According to one embodiment, the assembly comprises a plurality ofelongate enclosed channels.

Ideally, the channel is a microchannel, preferably an elongate enclosedmicrochannel.

Ideally, the semi-permeable membrane acts as a divider wall separatingthe elongate enclosed channel into a first channel and a second channel.In use, the first channel may receive sample cells and the secondchannel may receive analyte or vice versa. It will also be understood,that depending on the assay being carried out, both channels may receiveboth cells and analyte.

According to another embodiment, the biochip assembly for carrying outassays with living cells comprises at least one elongate enclosedchannel having a semi-permeable membrane mounted therein wherein thesemi-permeable membrane forms a connecting wall between at least twoadjoining channels. Ideally, the assembly comprises a first and secondchannel wherein the first channel receives said sample cells and thesecond channel receives said analyte.

The channel assembly of the invention may be arranged in severaldifferent ways. These type of constructions are described in more detailin relation to the figures.

For example, the adjoining channels may be in line and as such runparallel to each other. Alternatively, the adjoining channels mayintersect at one section of the channel only. Additionally, thesemi-permeable membrane abuts the elongate enclosed channel.

The semi-permeable membrane may permit unidirectional or bidirectionalflow.

In one embodiment, only a defined part or length of the channel is incontact with the said semi-permeable membrane.

In another embodiment, the semi-permeable membrane comprises one or moresemi-permeable membrane types characterized by different membraneproperties, for example each semi-permeable membrane type has adifferent pore size and/or different membrane size.

In yet another embodiment, at least one surface of the semi-permeablemembrane comprises one or more substances which effect cell function,preferably a substance which promotes the adhesion of cells. Thesemi-permeable membrane is ideally a microporous membrane.

Ideally, the semi-permeable membrane is a cell transparent membrane.Optionally, the cell transparent membrane may be seeded with cells. Thecell transparent membrane may be selectively permeable to different celltypes.

It is envisaged that the channel according to the invention willgenerally have a planar top wall to allow good optical properties forexamination under a microscope and generally speaking, the channelcomprises planar top, bottom and side walls (i.e. non-cylindricalcross-section).

It is also envisaged that assemblies comprising a plurality of biochipsas described above will be formed on one base sheet and will preferablyhave various common feeder channels having ports therein. This providesfor ease of examination under the microscope.

According to another aspect of the invention, there is a biochipassembly for carrying out assays with living cells wherein the assemblycomprises at least one elongate enclosed channel and a well wherein asemi-permeable membrane separates said channel from said well. Ideally,the semi-permeable membrane is mounted in the elongate enclosed channel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be more clearly understood with reference to thefollowing description given by way of example only and the followingnon-limiting figures. For clarity in viewing the drawings, wherepossible the same numbering for identical parts has been used in FIGS. 1to 15.

FIG. 1. is a plan view of a transmigration device of the inventionshowing the sample channel and analyte channel in line.

FIG. 2. is a side sectional view of the assembly along the lines A-A′ ofFIG. 1 showing the semi-permeable membrane separating the sample channelfrom the analyte channel.

FIG. 3. is a plan view of a transmigration device of the inventionshowing the sample channel and analyte channel crossing the analytechannel at one section comprising a semi-permeable membrane.

FIG. 4. is a side sectional view of the assembly along the lines A-A′ ofFIG. 1 showing two separate semi-permeable membranes and a singlecompression gasket separating the sample channel from the analytechannel.

FIG. 5. is a side sectional view of the assembly along the lines A-A′ ofFIG. 1 showing a semi-permeable membrane separating the sample channelfrom the analyte channel with two compression gaskets.

FIG. 6. is a side sectional view of the assembly along the lines A-A′ ofFIG. 1 showing the semi-permeable membrane separating the sample channelfrom the analyte channel. In this embodiment one of the channels depthis zero and the semi-permeable membrane abuts one of the channels,preferably the analyte channel. The analyte channel shown is coated withan ECM gel.

FIG. 7. is a plan view of a transmigration device of the inventionshowing multiple sample channels intersected by a single analytechannel.

FIG. 8. is a plan view of a transmigration device of the inventionshowing a single sample channel intersecting multiple analyte channels.

FIG. 9. is a plan view of a transmigration device of the inventionshowing multiple sample channels intersecting multiple analyte channels.Any number of channels may be used and the number of analyte channelsand sample channels may be the same or different.

FIG. 10. is a plan view of a transmigration device of the inventionshowing the sample channel and analyte channel in line and twosemi-permeable membrane types.

FIG. 11. is a side sectional view of the assembly along the lines A-A′of FIG. 1 showing the semi-permeable membrane separating the samplechannel from the analyte channel. In this figure cells are seeded on thesemi-permeable membrane.

FIG. 12 is a side sectional view of the assembly along the lines A-A′ ofFIG. 1 showing the semi-permeable membrane separating the sample channelfrom the analyte channel. In this figure a further layer of cells hasseeded itself on the cells previously seeded on the semi-permeablemembrane.

FIG. 13 is side sectional view of an alternative embodiment of theinvention showing a single channel separated from a well by asemi-permeable membrane.

FIG. 14 is an exploded perspective view of the construction of thetransmigration device showing the sample channel in line with theanalyte channel and where both channels are separated by asemi-permeable membrane.

FIG. 15 is an exploded perspective view of the construction of thetransmigration device through the intersection of the channels showingthe sample channel crossing the analyte channel at one sectioncomprising a semi-permeable membrane.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a device and method for performing cell-basedassays and cell tests. Prior to discussing this invention and figures infurther detail, the following terms used in the specification will firstbe explained.

The term “cell” includes both eukaryotic and prokaryotic cells,including but not limited to bacteria, yeast, mammalian cells. The useof plant cells may also be contemplated. Preferably the cells areeukaryotic cells. According to one particularly preferred embodiment thecells are leukocytes, such as neutrophils, lymphocytes etc.

The term “sample cells” or “sample cell containing liquid” ideallyrefers to a suspension of living cells within a suitable carrier medium,for example, a culture medium. Such a culture medium is ideally inliquid form but is not limited to this form. It will be understood thatmore than one type of cell may be in the suspension.

The semi-permeable membrane may be a cell-transparent membrane. Theseterms will be used interchangeably in the specification. The term “celltransparent membrane” encompasses a film or membrane that contains holesor pores large enough that at least some cells in the assays of interestcan traverse into the holes or pores and potentially migrate through themembrane. Ideally, these holes or pores are large enough for ameasurable fraction of the cells to traverse. An example of CellTransparent Membrane is the membrane manufactured by Millipore Inc,(www.millipore.com/cellbiology/cb3/microporousmembrane). Typically, themembrane may be made of polymer film, e.g. polycarbonate, hydrophilicPTFE, mixed cellulose, containing pores or holes of defined range ofdimensions. Ideally, the size of the holes in the membranes may be inthe range from approximately 1 μm to 20 μm in diameter. For certain celltypes, it will be understood that membranes containing holes of otherdimensions could also be used.

The membrane thickness is generally in the range from approximately 1 μmup to 1 mm, but more commonly is in the range from approximately 10 μmto 300 μm. The Cell Transparent Membrane is usually not hydraulicallytight, meaning that it cannot sustain a significant pressure differencebetween the two surfaces of the membrane in a liquid-tight manner.

The term “seeded cells” covers cells which are grown on thesemi-permeable membrane. These seeded cells may form a confluent ornon-confluent layer. Ideally, endothelial cells may be used as theseeded cells.

It will be understood that the semi-permeable membrane may be coatedwith a substance which alters the seeded cell function or promotesadhesion of the seeded cells to the semi-permeable membrane prior togrowth of the seeded cells. These substances may include cell adhesionsubstances and/or cell transmigration substances.

The term “reagent” or “reagent liquid”/“reagent gel” covers manydifferent types of analyte. The term “analyte” and “reagent” may be usedinterchangeably in the specification. The reagent may be achemoattractant, a toxic substance and/or a pharmaceutical preparation.For example, the reagent could be any liquid or gel from a drug underassessment, a poison, a cell nutrient, a liquid or gel containing othercells in suspension, reagent eluting cells or indeed any reagent whoseeffect on the sample cells requires assessment. It may also cover anyreagent which activates a defined cell function, such as a cell adhesionmolecule or cell transmigration molecule. In some embodiments of theinvention, the reagent may also be introduced into the sample cellchannel. The reagent gel may be in the form of a solid or semi-solidgel. For example, the reagent liquid may comprise ECM gel containingIL-8. It will also be understood that the reagent in certain cases maybe a placebo.

The term “cell function” means the biological or physiological functionof the cells such as cell mobility, cell attachment, cell detachment,cell apoptosis, metabolism, cell death due to the toxic effect of theenvironment, release of ligands, release of agents involved in cellsignaling, cell transmigration, adsorption of the chemicals and ligandsfrom the environment, change in the cell shape, cell rolling and otherbroadly similar functions.

The term “cell adhesion molecule” means any molecule which facilitatescell adhesion. These include among others members of the immunoglobulinsuperfamily (such as VCAM-1, ICAM-1, PECAM-1), selectins (such asE-selectin, P-selectin, L-selectin), catherins (such as E-catherin,N-catherin, P-catherin), integrins and any other molecule which willfacilitate adhesion of cells in the assay to the walls of the device orthe membrane. This also includes components of the extracellular matrixsuch as collagen, fibronectin, laminin. Any other suitable “celladhesion molecules” may also be contemplated.

The term “cell transmigration molecule” means any molecule that willactivate and facilitate the transmigration of the cells in the assay.This includes chemokines (CC chemokines-such as RANTES/CCL5, MCP-1/CCL2,CCL28; CXC chemokines-such as CXCL12; C chemokines-such as XCL1; CX3Cchemokines-such as fractalkine/CX3CL1) and any natural or syntheticmolecule that induces a cell to migrate. Any other suitable “celltransmigration molecules” may also be contemplated.

It will also be understood that the walls (i.e. the internal bore) ofthe channels, in their entirety or part thereof, may be coated withsubstances which interact with the sample cells. These substances mayinclude, but are not limited to enzymes, proteins, polysaccharides,glycoproteins, both natural and synthetic collagen. This may alsoinclude cell adhesion molecules and/or cell transmigration molecules. Tofacilitate the attachment of these substances to the walls of thefluidic channel it may be treated, e.g. by plasma treatment, so thatthey become hydrophilic. This type of treatment will be well known tothose skilled in the art.

The term “fluidic channel” or “elongate channel” covers a channelwherein the length of the channel is greater than the width/depth of thechannel. Ideally, such a channel has a width in the range fromapproximately 0.005 to 20 mm, more preferably in the range fromapproximately 0.1 to 10 mm and a depth in the range of fromapproximately 0.005 to 3 mm, more preferably in the range from 0.05 to0.5 mm. It will be understood that the width and the depth of thechannel do not need to be constant all across its entire length, andindeed may change considerably between different parts of the channel.

The channel is typically made in polymer material but indeed could alsobe made in glass or silicon or some other materials either opticallytransparent or non-transparent.

Furthermore, for ease of manufacturing the cross-section (internal bore)of the elongate channel is ideally non-cylindrical. In most embodimentsof this invention we will consider fluidic channels of rectangularcross-section. These are just convenient examples of fluidic channelcross-section that are easy to fabricate and more easy to describe andare by no means limiting. The fluidic channel cross-section could be ofany other shape, e.g. near rectangle with rounded corners, oval orsemicircle, etc. Ideally, the channel has a non-cylindricalcross-section. Furthermore, the cross-sectional area of the channel mayvary along its length.

Ideally, the channel of the invention has an internal bore ofapproximately 1 to 1000 micron in width, preferably 100 to 500 micron inwidth. Optionally, the bore of the channel may be substantiallyidentical to capillaries (e.g. of the order 8 microns), venules (e.g. ofthe order of 20 microns) or post capillary venules of a human or otheranimals for example.

It will be understood that the channel may be a “microfluidic channel”or “microchannel”, such as an “elongate enclosed microchannel”.Optionally, the internal bore of the microchannel, is substantially thesame size as the post capillary venules or capillaries of an animal, ormore particularly, a human. However, this is by no means limiting. Itwill be understood that post capillary venules have an internal bore ofbelow 50 micron in width.

As it will be readily appreciated by those skilled in the art, typicallyall the walls of a channel are liquid-tight. For example in the case ofa rectangular channel, the channel is comprised of four walls, all ofwhich are not transparent/permeable to the liquid transported by it. Incontrast, in our invention the fluidic channel may be defined in abroader way, wherein in some embodiments one or more walls of thefluidic channel can comprise a Cell Transparent Membrane and therefore,the channel is not necessarily liquid-tight. The channel does not needto be uniform along its entire length. For example, only a fraction ofthe length of the channel may comprise one wall comprising CellTransparent Membrane, while for the rest of the channel's length all ofits walls may be entirely liquid-tight. Furthermore, the channel maycontain membranes of several types. For example, one segment of thechannel may contain wall of membrane A and another segment of its lengthmay contain wall of membrane B having different properties.

The term “flow inducing means” encompasses devices which have theability to induce flow. Generally this means devices capable ofsupplying the pressure difference across fluidic channel. This may beaccomplished by means of syringes, various types of pumps, including thepump as described in the U.S. Pat. No. 6,805,841 (Shvets) which isincorporated herein by reference. The flow can also be induced by meansof electrophoretic or osmotic pumping. In preferred embodiment thepressure is induced by means of syringe pump or proprietary MirusNanopump® supplied by Cellix Ltd (www.cellixltd.com).

The term “fluidic device” or “biochip assembly” means a devicecomprising one or more channels or microchannels as defined above beingeither mutually coupled to each other or decoupled, one or more samplewells, one or more input ports and/or one of more output ports and/orthe coupling means such as tubing for coupling liquids in and out fromthe channels.

In the context of the present invention generally, the fluidic device isused for carrying out biological, medical, chemical, biochemical,biotechnology or drug discovery experiments or tests. The fluidic devicemay have one or more wells, sealed or unsealed integrated with thedevice that may be coupled into the channel(s) or decoupled from it(them). The fluidic device may be substantially planar, that is built ininto a substantially flat substrate or non-planar. The fluidic devicemay operate with external pumping means such as pump, syringe, pressuresource, electroosmotic pump. The fluidic device may have one or moresensors integrated into it. The device may be connected to the externalor internal pumping means by means of rigid or flexible tubing or anyother suitable connection means. The channels may be transparent tolight or opaque. They can be made of polymer material (e.g. PMMA,polystyrene, polycarbonate etc.), crystalline material (e.g. Si),amorphous material (e.g. glass) or a combination of several materialtypes.

It will be understood that the term “transmigration” does notnecessarily imply that the sample cells must migrate all the way acrossthe membrane from the sample cell containing channel to the reagentchannel. The transmigration of sample cells across the membrane is oneof the most common assays that can be carried out using the device.However, numerous other assays are also possible, including but notlimited to:

-   -   seeding the sample cells on the membrane, subjecting the sample        cells immobilized on the membrane to various chemical agents        injected either into the sample channel or the analyte channel,    -   observation of the response of the sample cells immobilized on        the membrane to the toxic agents injected at a known        concentration,    -   observation of the detachment of the immobilized sample cells        from the membrane back into the sample channel,    -   measurement of the shear force causing the detachment of the        immobilized sample cells from the membrane,    -   forming the layer of seeded cells on the membrane and        observation of interaction of the sample cells with the seeded        cells;    -   migration of the sample cell through the layer of endothelial        cell grown on the membrane;    -   observation of the detachment of the sample cells from the cells        seeded on the membrane;    -   observation of the attachment of the sample cells to the cells        seeded on the membrane.

Thus, the assay and method of the invention may be used in the study ofcell receptor-ligand interactions and cell-cell adhesion followed bycell migration.

Referring to the drawings, one embodiment of the transmigration deviceof the invention 1 is shown in FIG. 1. The device 1 comprises a samplechannel 3 and an analyte channel 6. In this figure, the sample channel 3and the analyte channel 6 are in-line and ideally run parallel. In theembodiment shown in FIG. 1 each of the two channels has one input (2,5)and one output (4,7). One could devise embodiments having more than oneinput and/or one output. The two channels are separated by asemi-permeable membrane 8, ideally a cell transparent membrane, such ase.g. polycarbonate membrane with pore size of 3, 5 or 8 um supplied byMillipore or Nucleopore. In the overlap region 15 the two channels areseparated merely by a membrane 8. In the embodiment shown in FIG. 1 theoverlap region extends for most of length of the channels. One couldalso devise an embodiment in which the overlap region covers only asmall segment of the channel's length.

It will be understood that the semi-permeable membrane 8 may permit thepassage of cells though it and as such may be a cell transparentmembrane. Passage of such cells may be unidirectional or bidirectional.

It will be understood that the channel is subjected to continuous flow(for example to mimic the flow of living cells in-vivo). Ideally, bothchannels are subjected to continuous flow in the same direction or inopposite directions. This assumes that both channels contain samplecells and reagent (analyte) in the form of liquid. If the reagent is inthe form of a gel, the analyte channel may be static.

FIG. 2 shows the cross-section A-A′ of the two channels of thetransmigration device 1 of FIG. 1. Effectively the cell transparentmembrane 8 serves as the section of the common wall of the two channels.The widths of the two channels (the sample channel and the analytechannel) and their depths can be identical or different. In someembodiments the channels are elongate enclosed microchannels. FIG. 2shows the two channels having the same width but this represents onlyone particular example of the transmigration device embodiment. Thus,the channels separated by a semi-permeable membrane may have differentwidths.

In one embodiment, the sample channel 3 and the analyte channel 6 can bemade by imprinting of a flat plastic substrate (e.g. ABS plastic, PEEK,PET, PMMA, polycarbonate, polypropylene etc) by means such as hotembossing, injection molding or lithographic pattern transfer technique.Ideally, the membrane 8 is in the form of a sheet and is positionedbetween two substrates, the sample substrate 9 and the analyte substrate11 which contain the sample channel 3 and the analyte channel 6respectively. In order to ensure a liquid tight connection, acompression gasket 13 of compressible polymer can be inserted in betweenthe inner surfaces of the two substrates (10, 12). FIG. 14 shows howthis particular construction may be assembled in practice.

It will be understood that the two channels, the sample channel 3 andthe analyte channel 6, do not have to be in-line or parallel to eachother, as shown in FIGS. 1, 2, 11 and 12. This is shown schematically inthe embodiment of the transmigration device shown in FIG. 3. They canoverlap, intersect or cross along an area (the overlap region) that issmall by comparison with the overall area of the channel. FIG. 15 showshow this particular construction may be assembled in practice.

Other embodiments of the invention can be contemplated, including,embodiments having more than one membrane 8 or more than one compressiongasket 13. For example, FIG. 4 shows an arrangement having twomembranes, 16 and 17 and one compression gasket 13. In this case theanalyte could be positioned in between the two membranes oralternatively two different types of cells could be seeded on themembranes 16 and 17. Alternatively, the membranes 16 and 17 could becovered by two different types of enzymes. Still alternatively, themembranes 16 and 17 could be membranes of different properties forexample different thickness or different extent of transparency to thetransmigrating cells. These advantages of the embodiment comprising twomembranes are given here by way of example only.

Many other configurations of experiments are possible. FIG. 5 showsembodiment of the transmigration device with one membrane 8 and twocompression gaskets 18 and 19. The advantage of this embodiment could bethat in some cases this transmigration device could be easiermanufactured as per embodiment utilizing two compression gaskets and onemembrane.

Many other embodiments could be readily devised by those skilled in theart, some are expanded on below as non-limiting examples of theinvention.

For example, in some embodiments the membrane could be laid against theflat inner surface of the substrate (e.g. sample substrate or analytesubstrate) and in others it could be bonded to that surface e.g. bymeans of adhesive or ultrasonic welding. FIG. 6 shows an embodiment ofthe transmigration device in which the depth of the analyte channel iszero. In this embodiment the semi-permeable membrane 8 abuts either oneof the channels. In this embodiment the analyte substrate is a flatsubstrate. The analyte substrate may be provided with a gel containing,for example, a cell transmigration reagent such as ECM gel 20. Thus, alayer of gel may be sandwiched between the semi-permeable membrane andthe analyte substrate.

With reference to FIG. 1, the sample channel input 2 and/or the analytechannel input 5 may be connected to a pumping means to provide cell flowand shear stress. In addition, the sample channel output 4 and/or theanalyte channel output 7 may be connected to the collection means suchas set of wells or collection reservoir. These are not shown in FIG. 1for brevity but will be well known to those skilled in this field andare described in the following U.S. Pat. Nos. 6,770,434, 6,805,841 and7,122,301 and U.S. patent application Ser. No. 10/500,277 by the sameinventors the contents of which are herein incorporated by reference.

The following describes one example of the operation of the device. Thewidth of both, the sample channel 3 and the analyte channel 6 is ideallyapproximately 400 μm and the channel depth is ideally approximately 100μm. The analyte channel is filled with an ECM gel containingapproximately 1-10 nM of IL-8 at the temperature of approximately 4degrees C. The gel in the analyte channel is allowed to solidify at thetemperature of 37 degrees C. for 30 minutes. Primary neutrophil cellswere isolated from the whole blood according to the protocol known tothose skilled in the field. The neutrophil cells were re-suspended in aculture medium, for example RPMI1640 (Gibco) at the concentration of 5million/ml and injected into the sample channel and flow at the averagelinear velocity of 0.83 mm/sec corresponding to the shear stress in therange of 0.5 dyne/cm². The sample cells 14 are schematically shown inFIG. 2. The flow/continuous flow can be supported by means of a suitablepump such as e.g. Mirus Nanopump™ from Cellix Ltd. The duration of theexperiment may be in the range of 20 minutes to 2 hours, although otherdurations may of course be contemplated. For the duration of the assay,transmigrating and resting neutrophil cells are supplied with a culturemedium (necessary to ensure cell viability and survival) through thesample channel 3. The cells migrating through the membrane are ideallyobserved by means of optical microscope and the number of cellsmigrating through the membrane is monitored by means of automatic imagerecognition software such as DucoCelI™ analysis software supplied byCellix Ltd. The results of the experiment can then be compared withreference results obtained under similar conditions, i.e. with thedifference being that the ECM gel in the analyte channel does notcontain IL-8.

Although, it is contemplated that a first channel of the device containsthe sample cells (the “sample channel”) and a second channel comprisesthe reagent (the “analyte channel”), the channels may also compriseadditional substances depending on the type of assay being carried out.For example, in order to ensure the sample cells are viable, it may benecessary to introduce a cell culture medium to the channel.Alternatively, liquid media may be needed to supply the cells withoxygen. Furthermore, it may be necessary to stain one or both of thechannels. Additionally, the reagent may be introduced into the channelmixed with a gel. Such gels may initially be in the form of a liquidthat turns into a gel as the temperature changes. Still additionally,one may want to test a drug candidate to assess changes totransmigration through the membrane caused by a chemoattractant.

In a preferred embodiment of the invention, sample cells are introducedinto one channel (e.g. first/sample channel) and a chemical agent thateffects their migration is introduced into a second channel (e.g.analyte channel). Such a chemical agent may be in the form of a gel, sothat the second channel/analyte channel is static. Optionally, thesemi-permeable membrane may have a layer of cells seeded on it, enablingthe study transmigration of cells through the seeded cell layer.

In an alternative embodiment of the invention, sample cells A may beintroduced into a first channel and reagent eluting sample cells B maybe introduced into a second channel. Each channel may also contain cellgrowth media. 2. Sample cells B may then release a reagent that causescells A to migrate from the first channel to the second channel. It willbe understood that many other configurations will be possible.

Further embodiments of the transmigration device are shown in FIG. 7, 8and 9. These embodiments comprise multiple intersections of sample andanalyte channels. For example, FIG. 7 shows the embodiment where oneanalyte channel 22 (analyte channel input 21 and analyte channel output23) crosses a number of sample channels 25 a to 25 e (sample channelinput 24 a to 24 e). The locations of intersections of the analytechannel 22 with the sample channels 25 a to 25 e include membranes asdescribed with reference to FIGS. 1 to 6. The membranes are not shown inFIG. 7. It will be understood that the widths of all the sample channelsdo not have to be identical. The sample channels can transport differentcell types (C₁, C₂, . . . , C_(n)) and in this way the transmigrationfunction could be tested in a variety of cell lines at the same timeagainst the same cell transmigration molecule. The sample channeloutputs are not shown in FIG. 7.

Likewise the same sample channel 27 (sample channel input 26) couldintersect a number of analyte channels 29 a to 29 d (analyte channelinput 28 a to 28 d, analyte channel output 30 a to 30 d) and thisembodiment is shown in FIG. 8. In this way the same cell type could betested against the variety of cell transmigration molecules. The samplechannel output is not shown in FIG. 8.

For example, consider FIG. 8, with the liquid in the sample channel 27moving downwards. Then there is increasing concentration of the samechemical in the analyte channels subsequent 1,2,3,4 marked with numerals29 a, 29 b, 29 c, 29 d, respectively, e.g. analyte channel 1 (29 a) hasconcentration x, channel 2 (29 b) : 5x, channel 3 (29 c): 25x, channel 4(29 d): 125x. Then the contamination from the analyte channel 1 (29 a)should be negligible as at the point of the analyte channel 2 (29 b)intersection with the sample channel, the concentration of the sameanalyte is much higher anyway. Likewise the concentration of the analytefrom the analyte channel 2 (29 b) at the cross section of analytechannel 3 (29 c) with the sample channel is also much smaller than theconcentration of the analyte directly from the analyte channel 3 (29 c),etc. In this manner cross-contamination is not an issue. In addition, ifthe reagent in the analyte channel is in the form of a gel,cross-contamination is not an issue as the gel would not be expected toelute much reagent into the sample channel.

In addition, another embodiment may comprise the intersection of avariety of sample channels 32 a to 32 e and analyte channels 34 a to 34f in one transmigration device 1 as schematically shown in FIG. 9. Inthis way the variety of cells could be simultaneously tested against thevariety of cell transmigration molecules. The sample channels outputsare not shown in FIG. 9. Sample channel inputs 31 a to 31 e are shownalong with analyte channel inputs 33 a to 33 f and analyte channeloutputs 35 a to 35 f.

FIG. 10 shows an embodiment of the transmigration device whereby thecell transparent membrane has several regions 36 and 37 each one beingcharacterized by a different set of membrane properties. For example,the membrane could comprise two areas each one being characterized by adifferent pore size. Alternatively, it could be comprised of two areashaving the same pore sizes but different membrane thickness. Theseregions are schematically marked in FIG. 10 as overlap region 1 (38) andoverlap region 2 (39). It will be understood that a single celltransparent membrane may have different membrane properties or whenmultiple membranes are used, each separate membrane may have differentproperties. If multiple membranes are used, they may form a continuousmembrane area or a non-continuous membrane area.

FIG. 11 shows another embodiment of the transmigration device where alayer of cells 40 is allowed to form on the membrane. The layer of cellscould be e.g. a confluent layer of endothelial cells. However, othercells could also be seeded on the membrane. Thus, in one embodiment, thelayer is a confluent layer of cells.

Alternatively, the layer of cells are non-confluent i.e. bare areascould be left on the membrane 8.

To seed the cells on the membrane 8, the membrane could be covered byspecific adhesion molecules such as fibronectin (Sigma Inc). Morepreferably the layer of cells is grown on the membrane when it isremoved from the transmigration device and placed into the cell cultureincubator at 37° C., 5% CO₂ and 80% humidity. Typically endothelialcells are seeded at the density of approximately 75000/cm² and allowedto grow for a period of 48 hours until a confluent layer of endothelialcell is formed. Different primary endothelial cells and cell lines mayrequire different density and seeding time. Following seeding, themembrane with seeded cells 40 is placed between the sample and theanalyte channels 3 and 6 and sealed by way of compression gasket 13.Subsequently, sample cells 14 are injected into the sample channel 3 andthe interaction between the sample cells 14 and the seeded cells 40 isobserved. This interaction could include by way of example the migrationof the sample cells through the layer of seeded cells, migration of thesample cells through the layer of seeded cells and thought the membrane,adhesion of the sample cells to the seeded cells.

In a further embodiment, the layer of the sample cells 14 could seed onthe layer of the seeded cells 40 as shown in FIG. 12. Then the samplecells 14 could be subjected to interaction with various chemicalsinjected either in the sample channel or the analyte channel. In yet afurther embodiment the layer of seeded cells as shown in FIG. 12 couldbe subjected to the chemical injected either in the sample channel 3 orin the analyte channel 6.

FIG. 13 shows an alternative embodiment of the device of the inventionin which one of the channels is a well 42. Ideally, the analyte channelis in the form of an open well 42, with no input or output. In thisembodiment, transmigration molecules may be in the form of a gel, whichis placed in the well 42. The semi-permeable membrane is placed at thebottom of the gel.

FIGS. 14 and 15 show expanded perspective views of the contraction ofthe devices of FIG. 1 and FIG. 3 respectively. These figures show howthe biochips 1 are made of sheets of plastic materials bonded together.Again, parts similar to those described, with reference to the previousdrawings, are identified by the same reference numerals. FIG. 14 showsthe channels (non-cylindrical bore) 3 and 6 formed in plastics materialsurrounding a sheet of membrane 8. The channels are in-line . FIG. 15shows the channels 3 and 6 separated by the sheet of membrane 8 crossingat a single intersection location.

Cells flowing through the channels may be observed via a microscope andimages may be captured and analysed at a later date. For this one coulduse conventional microscope or alternatively, a more specialistmiscroscope, such as confocal or fluoresecent microspe or indeed anyother microscope known in the field of cell imaging and analysis.

Various different imaging technologies can be used in conjunction withthe invention. Furthermore, various different image processingprogrammes for analysis and processing of the acquired images can alsobe used in conjunction with the invention. Finally, one could usepositive displacement or pressure driven pump to move cells and analytein the channels.

Some examples of these technologies and software follow.

For example, Cellix Ltd. has developed a novel Microfluidic Platformconsisting of a PC-controlled Nanopump® with microfluidic biochips (suchas Vena8® biochips (Cellix Ltd.) previously developed or the elongateenclosed channels of the invention) and DucoCell® (Cellix Limited)analysis software. The Nanopump® enables very accurate flow rates to beachieved which are more reproducible and consistent compared to anythingcurrently available. Importantly, flow rates are extremely low (5 pLmin-1 to 10 pL min-1) and the shear stress levels that the pump canmimic (up to 30 dyne cm-2) are equivalent to those found in bloodvessels in vivo. The Nanopump® is vital to the use of small diametercapillaries as standard syringe pumps are incapable of delivering therequired low flow rates.

In order to carry out an assay using the above platforms, the followinggeneral protocol may be used:

-   -   First of all, the cell type to be analysed must be determined,        followed by establishing how to harvest such cells e.g.        culturing in growth media, or isolation from in vivo fluids.    -   Secondly, the assay itself should be outlined, including whether        live cells or proteins will be coating the channels of the        biochip. If it is the former, protocols for culturing the cells        both outside and inside the biochip channel must be established.        Thirdly, the adhesion profile of the cells to be passed through        the coated channel should be determined.    -   Next, if exogenous compounds are being analysed, these should        then be introduced to the system and their effect on the        adhesion profile assessed.

This should include calculation of required concentrations andpre-incubation conditions, before introduction to the system. Finally,the images taken via the digital camera attached to the microscopeshould be masked and analysed using the Ducocell® software.

Various specific assays may be contemplated using these platformsincluding but not limited to:

-   -   A microfluidic assay assessing the effect of levocetirizine on        human eosinophil adhesion, involving the following        -   The method involves coating each microcapillary for one hour            in humid conditions at ambient temperature with either human            vascular cell adhesion molecule-1 (rhVCAM-1) or bovine serum            albumin (BSA) (both 10 μg mL-1 in HBSS containing Ca2+ and            Mg2+). All capillaries were then coated with BSA to occupy            non-specific binding sites. Resting or            Granulocyte-macrophage colony-stimulating factor            (GM-CSF)—treated eosinophils were pre-incubated at 37° C. in            a water bath for 10 mins before incubation with/without            levocetirizine (0.1 nM-100 nM), with anti-VLA-4 mAb as a            positive control) for a further 20 mins.        -   Eosinophils were infused into the capillaries (microfluidic            biochips) at stepwise increases in shear stress, from 0 to 5            dyne cm-2, one minute per shear stress level. Images at each            shear stress level were captured using the accompanying            PixeLINK microscopy software. For experiments with            GM-CSF-stimulated (1 ng mL-1) eosinophils, the cytokine was            added to the warmed cells at the same time as levocetirizine            and incubated at 37° C. for 20 mins prior to commencing the            flow assay. Adhesion was evaluated by monitoring eosinophil            migratory behaviour in real time with images captured via a            digital camera connected to the microscope.        -   Image analysis—several images per shear stress level may be            captured and adhered eosinophil numbers can be recorded            using Ducocell® application software. Data was exported into            Excel for interpretation. Statistical significance was            determined by Students unpaired t-test, and P>0.05 was            considered statistically significant. Data was presented as            mean±s.e.mean.    -   A microfluidic assay assessing the adhesion profiles of        peripheral blood lymphocytes (PBLs).    -   A microfluidic assay assessing the adhesion profile of platelets        on various matrix proteins.    -   A microfluidic assay assessing novel anti-inflammatory effects        of montelukast (MLK) on resting and GM-CSF-stimulated        eosinophils using the Cellix VenaFlux® platform to mimic        physiological adhesion to rhVCAM-1.    -   A microfluidic investigation of T-cell adhesion to ICAM-1 with a        mixed sepsis model treated with a range of statins under        physiological shear stress using the Cellix Microfluidic        Platform SP 1.0.        -   Cell Harvesting and Sample Treatments            -   Peripheral blood was donated by 6 healthy subjects.                Following mononuclear cell isolation, monocytes were                allowed to adhere to the culture vessels before B-cells                were removed from the T-cell population using nylon wool                adhesion.            -   T-cells were then co-cultured in the presence of                monocytes.            -   Cells were treated with 10 nM meva-, lova- or                simvastatin dissolved in ethanol (0.1% v/v final) or                prava- or fluvastatin dissolved in water. Cells were                then stimulated with 2 μg/ml lipopolysachharide (LPS)                and 20 μg/ml peptidoglycan G (PepG). Control cells were                treated with 0.1% v/v ethanol±LPS/PepG and incubated a                humidified 37° C. incubator containing 5% CO2 for 18                hours.        -   Biochip Coating Procedures            -   Each microchannel (400 μm wide, 100 μm deep) was coated                overnight in humid conditions at 4° C. with rhICAM-1 (10                μg/ml), before being coated with BSA, 10 μg/ml. Two                additional channels were coated with BSA for 2 hrs at                room temperature. Prior to shear experiments, all                channels were washed thrice with media.        -   Adhesion Profiles            -   Isolated T cells were infused into the rhICAM-1 and BSA                coated channels under a defined shear stress of 0.5 dyne                cm-2 for a time period of 5 minutes in CO2 independent                media.            -   Images were captured using the accompanying PixelLink                imaging software.        -   Image Analysis            -   T cell adhesion profiles of single cells were recorded                using DucoCell® software. Cell images were captured from                three microscopic fields from each channel. Data was                exported into Excel to allow further analysis.        -   Statistics            -   Data obtained from this experiment can be analyzed using                the Wilcoxon's signed-rank test using Graphpad Prism® 4                software.    -   A microfluidic assay to elucidate the importance of        physiological shear stress environment required for E. coli        adhesion, colonisation and biofilm formation using the Cellix        VenaFlux® Platform.        -   Biochip Coating Procedure:            -   Each microchannel (400 μm wide, 100 μm deep) was coated                in humid conditions at 37° C. for 45 min with 10 μl of                either 200 μg/ml mannose-BSA (monomannase), 20 μg/ml                RnaseB (trimannose); or 10% BSA. Prior to flow                experiments each channel was washed three times with                PBS-0.2% BSA and quenched with PBS-0.2% BSA for 15 min                to decrease non-specific binding.        -   Adhesion Profiles:            -   Bacteria was infused into the 1M, 3M and BSA coated                channels using pre-defined shear steps from 0.1, 0.3,                1.0 and 8.0 dyne/cm², 100 s per shear stress level.        -   Image Analysis:            -   E. coli adhesion profiles of single cells were recorded                using MetaMorph software. Cell images were captured from                three microscopic fields from each channel and further                analysed by Image J and Cellix's DucoCell® software.                Data was exported into Excel to allow further analysis.    -   A microfluidic assay to examine differential cell adhesion        within an isogenic model of melanoma progression under        physiological shear flow conditions using the Cellix VenaFlux™        Platform.    -   A microfluidic assay to screen a range of novel thermoresponsive        polymers designed to be used as dual drug-eluting systems in        coating stents. Specifically, to assess the ability of        xemilofiban released in conjunction with fluvastatin, to prevent        thrombus formation/platelet adhesion to fibrinogen using        Cellix's VenaFlux® platform.

It will be understood that the device described may be called atransmigration device. As explained above, this term does not imply thatthe sample cells must migrate all the way across the membrane from thesample channel into the analyte channel. Such a transmigration of samplecells across the membrane is indeed one of the most common assays thatcan be carried out using the device. However, we also described numerousother assays such as seeding the sample cells on the membrane,subjecting the sample cells immobilized on the membrane to variouschemical agents injected either into the sample channel or the analytechannel, observation of the response of the sample cells immobilized onthe membrane to the toxic agents injected at a known concentration,observation of the detachment of the immobilized sample cells from themembrane back into the sample channel, measurement of the shear forcecausing the detachment of the immobilized sample cells from themembrane, forming the layer of seeded cells on the membrane andobservation of interaction of the sample cells with the seeded cells;migration of the sample cell through the layer of endothelial cell grownon the membrane; observation of the detachment of the sample cells fromthe cells seeded on the membrane; observation of the attachment of thesample cells to the cells seeded on the membrane. Thus, the device ofthe invention may be used to carry out multiple assays on living cells,the transmigration aspect is merely a preferred embodiment of theinvention.

In the specification, the terms “comprise, comprises, comprised andcomprising” or any variation thereof and the terms “include, includes,included and including” or any variation thereof are considered to betotally interchangeable and they should all be afforded the widestpossible interpretation.

The invention is not limited to the embodiment hereinbefore described,but may be varied in both construction and detail within the scope ofthe claims.

1. A method for measuring the migration of cells in a channel under the influence of an analyte wherein said cells are separated from said analyte by a semi-permeable membrane and said analyte and/or said cells are subjected to controlled flow conditions.
 2. The method of claim 1 wherein the method takes place in an elongate enclosed channel having a semi-permeable membrane mounted therein.
 3. The method of claim 1 wherein said cells are present on at least one side of said semi-permeable membrane and said analyte is present on the opposed surface thereto.
 4. The method of claim 1 wherein said sample cells and/or said analyte are introduced into the channel at a controlled steady flow rate.
 5. The method of claim 1 wherein said cells or said analyte on one side of said membrane is subjected to controlled flow.
 6. The method of claim 1 wherein said cells or said analyte on both sides of said membrane are subjected to controlled flow.
 7. The method of claim 1 wherein said channel is a microchannel.
 8. The method of claim 1 wherein said analyte is a reagent liquid or gel or a reagent eluting cell.
 9. The method of claim 1 further comprising forming a layer of seeded cells adjacent to at least one side of said semi-permeable membrane.
 10. The method of claim 9 wherein said layer of seeded cells is formed and mounted in the channel prior to use.
 11. The method of claim 1 further comprising coating at least one side of the semi-permeable membrane with one or more substances which effect cell function prior to forming a layer of seeded cells on said semi-permeable membrane.
 12. The method of claim 11 wherein the substance promotes adhesion of cells.
 13. The method of claim 11 wherein the substance is in the form of a gel.
 14. The method of claim 9 wherein the seeded cells form either a confluent or non-confluent layer adjacent to said semi-permeable membrane.
 15. The method of claim 9 wherein the interaction between said seeded cells and said sample cells is monitored and/or recorded.
 16. The method of claim 1 comprising a further step of coating the internal bore of the channel prior to use with a substance which interacts with said seeded and/or sample cells, preferably a cell adhesion molecule and/or a cell transmigration substance.
 17. The method of claim 16 wherein the physiological function of said seeded cells is monitored and/or recorded.
 18. The method of claim 9 wherein the physiological function of said seeded cells is measured as a function of the shear stress within the channel.
 19. The method of claim 1 comprising introducing analyte to said channel and monitoring and/or recording the response of said seeded cells and/or sample cells to said analyte, in terms of adsorption, metabolism and/or toxicity.
 20. The method of claim 1 or claim 9 wherein cell to cell interactions and cell to analyte interactions are measured.
 21. The method of claim 1 wherein the flow is sustained by a pressure driven pumping system or a positive displacement pumping system.
 22. A biochip assembly for carrying out assays with living cells wherein the assembly comprises at least one elongate enclosed channel having a semi-permeable membrane mounted therein.
 23. The biochip assembly of claim 22 comprising a plurality of elongate enclosed channels.
 24. The biochip assembly according to claim 22 for carrying out assays with living cells wherein the assembly comprises at least one elongate enclosed channel having a semi-permeable membrane mounted therein wherein the semi-permeable membrane acts as a divider wall separating the elongate enclosed channel into a first channel and a second channel
 25. The biochip assembly of claim 24 wherein the first channel receives sample cells and the second channel receives analyte or vice versa.
 26. A biochip assembly for carrying out assays with living cells wherein the assembly comprises at least one elongate enclosed channel having a semi-permeable membrane mounted therein wherein the semi-permeable membrane forms a connecting wall between at least two adjoining channels.
 27. The assembly of claim 26 comprising a first and second channel wherein the first channel receives said sample cells and the second channel receives said analyte.
 28. The assembly of claim 26 wherein the adjoining channels are in line.
 29. The assembly of claim 26 in which the adjoining channels intersect at one section only.
 30. The assembly of claim 24 wherein the semi-permeable membrane abuts the elongate enclosed channel.
 31. The assembly of claim 24 wherein the semi-permeable membrane permits unidirectional or bidirectional flow.
 32. The assembly of claim 24 wherein part of the channel is in contact with said semi-permeable membrane.
 33. The assembly of claim 24 wherein said semi-permeable membrane comprises one or more semi-permeable membrane types characterized by different membrane properties.
 34. The assembly of claim 33 wherein each semi-permeable membrane type has different pore size and/or different membrane size.
 35. The assembly of claim 24 wherein at least one surface of the cell transparent membrane comprises one or more substances which effect cell function, preferably a substance which promotes the adhesion of cells.
 36. The assembly of claim 24 wherein the semi-permeable membrane is a cell transparent membrane.
 37. The assembly of claim 37 wherein the cell transparent membrane is seeded with cells.
 38. The assembly of claim 37 wherein the cell transparent membrane is selectively permeable to different cell types.
 39. A biochip assembly for carrying out assays with living cells wherein the assembly comprises at least one elongate enclosed channel and a well wherein a semi-permeable membrane separates said channel from said well. 